JP-A-1-152369 (1989) and JP-A-2-134570 (1990) which corresponds to U.S. Pat. Application Ser. No. 07/429,546, now U.S. Pat. No. 5,095,752, disclose conventional capacitive type semiconductor accelerometers in which the detecting arrangement is constituted by laminating three layers, including an upper glass plate, intermediate silicon plate and lower glass plate.
In the above conventional capacitive type semiconductor accelerometers, no sufficient consideration was made in connection with the lead out arrangement of the leads from the stationary electrodes formed on the upper and lower glass plates, such that there were problems with respect to their mass production and reliability.
Hereinbelow problems concerning mass production are enumerated more specifically.
(1) It was necessary to form a through hole in the glass plate for leading out the lead from the stationary electrode formed on the upper glass plate.
(2) The process for forming a conductive portion inside the though hole was complex which was needed for electrical connection between pads for wire bonding and the stationary electrodes.
(3) It was necessary to form a square shaped aperture in a part of the upper glass plate because each pad for the wire bonding was respectively arranged on the upper glass plate, intermediate silicon plate and lower glass plate.
(4) The wire bonding work for electrically connecting the pads to a signal processing circuit was difficult because there were steps between respective pad portions. Further, the formation of the pads via sputtering after anodic bonding of the upper glass plate, intermediate silicon plate and lower glass plate was difficult because of the steps between the pad portions.
(5) It was necessary to completely seal the through hole after the anodic bonding for preventing water and dust from intruding when obtaining a detecting chip for the accelerometer via dicing. Further, for electrically insulating the lead portion of the stationary electrode formed on the lower glass plate from the intermediate silicon plate, grooves were formed on a part of the intermediate silicon plate by anisotropic etching. As a result it was also necessary to completely seal the groove portions formed on the lower face of the intermediate silicon plate by means of an aperture formed in the upper glass plate for further preventing water and dust from intruding through the groove portions.
Further insufficient reliability resulted for the reasons as follows:
When forming the conductive portions inside the through holes such as by sputtering, disconnection of the conductive portions at edges of the through holes is likely to be caused due to slight change of its process condition.